The field to which this invention pertains is curable compositions based on mixtures of polyepoxide-amine adducts and epoxy resins, particularly aqueous compositions wherein the epoxy resin is microemulsified in an aqueous solution of an acid salt of the polyepoxide-amine adduct.
Industrial maintenance coatings are used as protective coatings for a variety of substrates which are exposed to harsh environmental or use conditions. Such coatings should exhibit chemical and stain resistant properties, gloss and hardness, as well as good adhesion to the substrates to which they are applied. Improved adhesion is attained when the coatings are capable of wetting a substrate to which they are applied. Such coatings must provide a sealing film over a variety of substrates such as metals, wood, wall board, concrete, and various masonry surfaces. Moreover, such coatings must be capable of being cured at normal ambient temperatures since it is not always convenient to subject the coated substrate to elevated temperatures.
Due to increasing problems with air pollution, considerable efforts are being expended to convert organic solvent containing coating compositions to water based systems, i.e., coating systems based on solutions, dispersions and emulsions of film forming resins in water. One of the problems in the use of aqueous systems is the inability of the resin to properly wet the substrate and to form a continuous coating. Another problem is the low water and solvent resistance of the coatings which are cured at ambient temperatures. Still other problems are the mechanical stability, e.g., particle settling, freeze-thaw stability and shear sensitivity, and chemical stability, e.g., pot-life, of aqueous coating systems.
The mechanical stability, e.g., particle settling, freeze thaw stability, shear sensitivity, and chemical stability, e.g., pot-life and sag resistance as a function of pot life, of aqueous coating systems as well as the chemical and physical properties of an applied coating derived therefrom, such as cure time and temperature, gloss, blush resistance, and wet adhesion, etc., will vary not only with the identity of the polymers present therein but also with the particular physical arrangement of distribution of these polymers in the aqueous media. For example, generally, the smaller the particle size of the film forming components of a paint composition the better will be the coalescence of these particles upon drying and the better will be the continuity and gloss of the resulting film. However, if the particle size is too small, the components can be excessively reactive and can also require substantial amounts of water to attain application viscosity, thereby lowering the solids content of the system. Consequently, it is desirable to formulate a particular coating system wherein the polymers present therein possess a small particle size which is tailored to the needs of the system. When the film forming components are soluble in water, pot life is excessively short and particle size is not adjustable. However, when one or more of the film forming components are insoluble in water, particle size becomes a factor to be controlled.
One approach to water based systems involves emulsification of the resins, e.g., epoxy resins, themselves. However, when such emulsions or dispersions are combined with curing agents, e.g., polyamide-amines, or carbonate forming polyamines, incompatability can result upon coalescence which can be manifested by undesirable loss of film gloss and by permeability to water and aggressive chemicals.
Moreover, when excessive amounts of emulsifying agents are employed to achieve a suitable reduction in the particle size of the film forming components, the water resistance and hardness of the resulting film is reduced.
The search has continued for an aqueous based coating composition which can be employed as an industrial maintenance coating and which, when applied as a film, exhibits certain desirable characteristics. The present invention is a result of this search.
It is an object of the present invention to provide a relatively solvent free coating system which meets current air pollution regulations.
It is a further object of the present invention to provide a coating system which is capable of exhibiting a commercially acceptable pot life, improved wetting properties, and compatability of the components present therein, and will cure at normal ambient temperatures.
It is still another object of the present invention to provide a coating system which is capable of forming films having improved gloss, water resistance, alkali resistance, solvent resistance, flash rusting resistance, good adhesion properties, early tack free time, and good overnight hardness.
These and other objects and features of the invention will become apparent from the claims and from the following description.